Developing ASCL1 and NEUROD1 lineage oncogene targeted therapy for small cell lung cancer (SCLC) This application focuses on developing new targeted therapy for SCLC focusing on two key lineage oncogenes involved in SCLC pathogenesis and malignant behavior, ASCL1 and NEUROD1. Nearly 90% of SCLCs express ASCL1, NEUROD1 or both. In the preclinical models, including human SCLC lines and xenografts and genetically engineered mouse models (GEMMs) of SCLC, tumors that express either ASCL1 or NEUROD1 appear ?addicted? to their expression and function. The presence of ASCL1 or NEUROD1 also are associated with expression of important downstream oncogenes and regulatory genes. If ASCL1/NEUROD1 are removed (through genetic knockdown) SCLCs undergo many logs of tumor cell kill. Using state of the art technology in human preclinical models, we propose to systematically study the dependency of a large number of SCLC lines and xenografts (including patient derived xenografts, PDXs, and circulating tumor cell derived xenografts, CDXs) on ASCL1 and NEUROD1 through genetic knockdown, and systematically test the ability of blocking genetically and pharmacologically downstream potentially ?druggable? targets of these two transcription factors to kill SCLCs. We have three specific aims: Aim 1. Determine ASCL1 and NEUROD1 expression patterns and clinical and molecular correlates in preclinical SCLC models and tumor specimens; Aim 2. Determine ASCL1 and NEUROD1 genetic dependency phenotypes, potential molecular biomarkers predicting response, and frequency and mechanisms of resistance in SCLC preclinical models; Aim 3. Determine the role of ASCL1 and NEUROD1 directly regulated ?downstream? targets as vulnerabilities that can be exploited for therapeutic effect using in vivo xenograft shRNA mini-library ?drop out? screens and selected drugs that inhibit downstream ?druggable? targets. As part of these aims we will also determine if resistance to ASCL1 or NEUROD1 targeted therapy in SCLCs develops using CRISPR-CAS9 technology including potential mechanisms of this resistance, and we will explore the possible use of ASCL1 and NEUROD1 expression as SCLC enrollment biomarkers for developing ?precision medicine? to predict the response of such targeted therapy in individual SCLCs. We have developed a large amount of preliminary data on which this application is based including 1) assembling the world?s largest collection of clinically and molecularly annotated human SCLC lines and xenografts, as well as important GEMMs of SCLC, 2) generating a comprehensive list of directly regulated downstream targets of ASCL1 and NEUROD1 through ChipSeq/RNASeq and chromatin landscape studies, and 3) developing experimental approaches to systematically study the dependency of SCLCs on ASCL1 and NEUORD1 downstream targets. We have assembled a world class team of investigators, including a patient advocate, with complementary skills to assure the successful completion of this project. The final deliverables will serve as the basis for new ASCL1 and NEUROD1 targeted therapeutics for SCLC.